A nickel dimethyl glyoximato complex to form nickel based nanoparticles for electrocatalytic H2 production

Computational investigation into intramolecular hydrogen bonding controlling the isomer formation and pKa of octahedral nickel (II) proton reduction catalysts

This work demonstrates the impact of intramolecular hydrogen bonding (H-bonding) on the calculated pKa of octahedral tris-(pyridinethiolato)nickel (II), [Ni(PyS)3]-, proton reduction catalysts. Density Functional Theory (DFT) calculations on a [Ni(PyS)3]-...

Successes, challenges, and opportunities for quantum chemistry in understanding metalloenzymes for solar fuels research

Overview of the rich and diverse contributions of quantum chemistry to understanding the structure and function of the biological archetypes for solar fuel research, photosystem II and hydrogenases.

The odyssey of cobaloximes for catalytic H2 production and their recent revival with enzyme-inspired design

Cobaloxime complexes gained attention for their intrinsic ability of catalytic H₂ production despite their initial emergence as a vitamin B12 model. The simple, robust, and synthetically manoeuvrable cobaloxime core represents a model catalyst molecule for the investigation of optimal conditions for both photo- and electrocatalytic H₂ production catalytic assemblies. Cobaloxime is one of the rare catalysts that finds equal applications in the analysis of homogeneous and heterogeneous catalytic conditions. However, the poor aqueous solubility and long-term instability of cobaloximes have severely impeded their growth. Lately, interest in the cobaloxime-based catalysts has been resuscitated with the rational use of extended enzymatic features. This unique enzyme-inspired catalyst design strategy has instigated the formation of a new genre of cobaloxime molecules that exhibit enhanced photo- and electrocatalytic H₂ evolution with improved aqueous and air stability.

Ligand-based electronic effects on the electrocatalytic hydrogen production by thiosemicarbazone nickel complexes

This work reports on the synthesis and characterization of a series of mononuclear thiosemicarbazone nickel complexes that display significant catalytic activity for hydrogen production in DMF using trifluoroacetic acid as the proton source.

Molecular Electrocatalysts for the Hydrogen Evolution Reaction: Input from Quantum Chemistry

In the pursuit of carbon-free fuels, hydrogen can be considered as an apt energy carrier. The design of molecular electrocatalysts for hydrogen production is important for the development of renewable energy sources that are abundant, inexpensive, and environmentally benign. Over the last 20 years, a large number of electrocatalysts have been developed, and considerable efforts have been directed toward the design of earth-abundant, first-row transition-metal complexes capable of promoting electrocatalytic hydrogen evolution reaction (HER). In this context, numerical approaches have emerged as powerful tools to study the catalytic performances of these complexes. This review covers some of the most significant theoretical mechanistic studies of biomimetic and bioinspired homogeneous HER catalysts. The approaches employed to study the free energy landscapes are discussed and methods used to obtain accurate estimates of relevant observables required to study the HER are presented. Furthermore, the structural and electronic parameters that govern the reactivity, and are necessary to achieve efficient hydrogen production, are discussed in view of future research directions.

Effect of Stacking Interactions on the Translation of Structurally Related Bis(thiosemicarbazonato)nickel(II) HER Catalysts to Modified Electrode Surfaces

A series of crystalline nickel(II) complexes (1-3) based on inexpensive bis(thiosemicarbazone) ligands diacetylbis(4-methyl-3-thiosemicarbazone) (H₂ATSM), diacetylbis(4,4-dimethyl-3-thiosemicarbazone) (H₂ATSDM), and diacetylbis[4-(2,2,2-trifluoroethyl)-3-thiosemicarbazone] (H₂ATSM-F₆) were synthesized and characterized by single-crystal X-ray diffraction and NMR, UV-visible, and Fourier transform infrared spectroscopies. Modified electrodes GC-1-GC-3 were prepared with films of 1-3 deposited on glassy carbon and evaluated as potential hydrogen evolution reaction (HER) catalysts. HER studies in 0.5 M aqueous H₂SO₄ (10 mA cm^-2) revealed dramatic shifts in the overpotential from 0.740 to 0.450 V after extended cycling for 1 and 2. The charge-transfer resistances for GC-1-GC-3 were determined to be 270, 160, and 630 Ω, respectively. Characterization of the modified surfaces for GC-1 and GC-2 by scanning electron microscopy and Raman spectroscopy revealed similar crystalline coatings before HER that changed to surface-modified crystallites after conditioning. The surface of GC-3 had an initial glasslike appearance before HER that delaminated after HER. The differences in the surface morphology and the effect of conditioning are correlated with crystal-packing effects. Complexes 1 and 2 pack as columns of interacting complexes in the crystallographic a direction with short interplanar spacings between 3.37 and 3.54 Å. Complex 3 packs as columns of isolated molecules in the crystallographic b direction with long-range interplanar spacings of 9.40 Å.

On decomposition, degradation, and voltammetric deviation: the electrochemist's field guide to identifying precatalyst transformation

What is the identity of the true electrocatalytic species?

Ni(ii) complexes of the phosphine-oxime Ph2PC6H4-2-CH[double bond, length as m-dash]NOH

We report the solution and structural chemistry of nickel(ii) complexes of the phosphine-oxime Ph2PC6H4-2-CH[double bond, length as m-dash]NOH (PCH[double bond, length as m-dash]NOH). PCH[double bond, length as m-dash]NOH invariably binds in a bidentate manner as illustrated by cis-Ni(PCH[double bond, length as m-dash]NOH)2Cl2 and cis-[Ni(PCH[double bond, length as m-dash]NOH)2]2+ (as its BF4- salt). Treatment of PCH[double bond, length as m-dash]NOH with Ni(OAc)2(H2O)4 gave charge-neutral trans-[Ni(PCH[double bond, length as m-dash]NO)2]0. Treatment of trans-[Ni(PCH[double bond, length as m-dash]NO)2]0 with BF3 gave [Ni(PCH[double bond, length as m-dash]NO)2BF2]BF4. The cation features a planar NiP2N2 center wherein the pair of oximate groups are linked by the difluoroboryl center. The 1 : 1 complexes of the oxime and the oximate are illustrated by [Ni(PCH[double bond, length as m-dash]NOH)Cl2]2 and [Ni(C6F5)(PCH[double bond, length as m-dash]NO)]2, which feature five- and four-coordinate Ni(ii) centers, respectively. All complexes in this series hydrolyze to give the trinickel oxo-phosphine-oximate complex [Ni3(PCH[double bond, length as m-dash]NO)3O]+. One feature of the PCH[double bond, length as m-dash]NOH ligand is its wide bite angle combined with its protic OH center. These aspects are manifested in the structures of Ni(PCH[double bond, length as m-dash]NOH)2Cl2 and [Ni(PCH[double bond, length as m-dash]NOH)Cl2]2, which show intramolecular hydrogen bonding to terminal chloride ligands.

Dye synthesis in the Pechmann reaction: catalytic behaviour of samarium oxide nanoparticles studied using single molecule fluorescence microscopy

Photochemically prepared samarium oxide nanoparticles (Sm₂O₃NP) efficiently catalyze the formation of coumarin 153 via the Pechmann trans-esterification and condensation process. The formation of the fluorescent coumarin allowed the catalytic process to be monitored in real time at the single molecule level using Total Internal Reflection Fluorescence Microscopy (TIRFM). Benchtop experiments conducted in parallel demonstrated that the observed catalysis occurred in solution rather than by pure heterogeneous catalysis and is due to a mobile population of small Sm₂O₃NP released from a polydisperse original sample containing larger particles. TIRFM provided unique insights by demonstrating that catalysis by these smaller colloidal particles is in fact a surface process, while the larger particles are merely suppliers of the small catalytic nanostructures. We refer to this behaviour as a semi-heterogeneous catalytic system. This work showcases the opportunity that single molecule fluorescence techniques can offer in terms of understanding and ultimately improving benchtop and scaled-up synthesis. This specific example highlights the general applicability of this approach to the study of widely-utilized chemical reactions and lays the groundwork for researchers to adopt similar strategies in other systems.

Electrochemical hydrogenation of a homogeneous nickel complex to form a surface adsorbed hydrogen-evolving species

A Ni(II) complex degrades electrochemically in the presence of acid in acetonitrile to form an electrode adsorbed film that catalytically evolves hydrogen. Comparison with a similar compound permitted investigation of the degradation mechanism.

Synthetic Active Site Model of the [NiFeSe] Hydrogenase

A dinuclear synthetic model of the [NiFeSe] hydrogenase active site and a structural, spectroscopic and electrochemical analysis of this complex is reported. [NiFe(‘S₂Se₂’)(CO)₃] (H₂‘S₂Se₂’=1,2-bis(2-thiabutyl-3,3-dimethyl-4-selenol)benzene) has been synthesized by reacting the nickel selenolate complex [Ni(‘S₂Se₂’)] with [Fe(CO)₃bda] (bda=benzylideneacetone). X-ray crystal structure analysis confirms that [NiFe(‘S₂Se₂’)(CO)₃] mimics the key structural features of the enzyme active site, including a doubly bridged heterobimetallic nickel and iron center with a selenolate terminally coordinated to the nickel center. Comparison of [NiFe(‘S₂Se₂’)(CO)₃] with the previously reported thiolate analogue [NiFe(‘S₄’)(CO)₃] (H₂‘S₄’=H₂xbsms=1,2-bis(4-mercapto-3,3-dimethyl-2-thiabutyl)benzene) showed that the selenolate groups in [NiFe(‘S₂Se₂’)(CO)₃] give lower carbonyl stretching frequencies in the IR spectrum. Electrochemical studies of [NiFe(‘S₂Se₂’)(CO)₃] and [NiFe(‘S₄’)(CO)₃] demonstrated that both complexes do not operate as homogenous H₂ evolution catalysts, but are precursors to a solid deposit on an electrode surface for H₂ evolution catalysis in organic and aqueous solution.

Electrode initiated proton-coupled electron transfer to promote degradation of a nickel(ii) coordination complex

A Ni(ii) bisphosphine dithiolate compound degrades into an electrode-adsorbed film that can evolve hydrogen under reducing and protic conditions. An electrochemical study suggests that the degradation mechanism involves an initial concerted proton-electron transfer. The potential susceptibility of Ni-S bonds in molecular hydrogen evolution catalysts to degradation via C-S bond cleavage is discussed.

DFT analysis into the intermediates of nickel pyridinethiolate catalysed proton reduction

The catalytic cycle of the water reduction catalyst, nickel pyridine 2-thiolate, has been investigated using Density Functional Theory.

A nickel complex of a conjugated bis-dithiocarbazate Schiff base for the photocatalytic production of hydrogen

A nickel complex containing a conjugated bis-dithiocarbazate ligand is an active catalyst for the reduction of protons into hydrogen gas.